PHPMaster.com is back with the third part of their series looking at the internals of the Yii framework (specifically, its components). In this latest article Steven O'Brien focuses on how the framework uses behaviors.

A behavior, as it is called in Yii, is a manner of combining objects at runtime to extend an object’s functionality. Behaviors are an excellent way to decouple code and keep ever expanding systems maintainable. [...] We can not reuse our code effectively because PHP doesn’t support multiple inheritance. The Yii behavior system is a way of achieving multiple inheritance by implementing mixins.

He gives an example of working with a user that's connecting to your application just to get to a third-party billing system. They show how to take this functionality our of your generic "User" class and make a behavior out of it. This functionality can then be attached to the User object (via an attachBehavior call) and used directly. He gets into how Yii does this magic, showing how it appends it to a special value in the class and the __call method checks the method call to see if it exists in one of these special classes.